Background: Weight loss and undernutrition are common in patients with Alzheimer's disease (AD) and associated with negative health outcomes. In the current guidelines on diagnosis and treatment of AD, no recommendations for treatment of (risk of) undernutrition in community-dwelling AD patients are given. Methods: We conducted a systematic review on the effect of nutritional interventions in community-dwelling AD patients with (risk of) undernutrition, according to the methods outlined by the Cochrane Collaboration. Three electronic databases and three trial registers were searched from inception till April 2013. Results: Literature search in the electronic databases yielded 546 records of which one was relevant for this review. This study, with a high risk of bias, demonstrated that oral nutritional supplements improved nutritional outcomes without effect on clinical and biochemical outcomes. The search in the trial registers yielded 369 records of which two were relevant. One trial was terminated because of failing inclusion, the other is ongoing. Conclusions: This systematic review on the effect of nutritional interventions in community-dwelling AD patients with (risk of) undernutrition, reveals a serious lack of evidence. Therefore, it is not possible to state what the best approach is.